Information is vital in today's fast-paced world. The plethora of information, such as phone numbers, fax numbers, birthdays, anniversaries, and e-mail addresses, can be overwhelming. Many people use calculator-sized personal information managers to help them organize information that is important to them. Personal information managers can be used to store and access the information that people desire to have at their fingertips.
Although calculator-sized personal information managers are widely popular, their size and shape often make them inconvenient to transport from place to place and easy to misplace. Therefore, a personal information manager, incorporated into a wristwatch, has been developed that is more convenient to transport than a calculator-sized personal information manager. However, one problem encountered in the development of wristwatch personal information managers was the entry of information. A calculator-sized personal information manager usually has a keyboard to enter information into the device. However, a wristwatch personal information manager that includes a keyboard is either too large to wear comfortably or has keys so small that it is difficult to depress the keys to enter information into the wristwatch. Therefore, systems for transmitting information to the wristwatch personal information manager that do not require a keyboard were developed.
One known system for transmitting information to a wristwatch personal information manager is the "DATALINK" wristwatch personal information manager system from Timex Corporation of Middlebury, Conn. In the "DATALINK" system, a program module running on a personal computer includes information such as appointments, phone numbers, etc. The program module can be used to download the information from the program module to a wristwatch personal information manager so that this information can be accessed when the user is away from his personal computer. To download information, the wristwatch personal information manager has an optical sensor that receives a serial bit transmission in the form of light pulses at a fixed bit rate from the monitor of the personal computer.
To facilitate an understanding of data transmission in the "DATALINK" system, the basic operation of a display device will be described below. A display device, such as a cathode ray tube (CRT), typically includes an electron gun and a screen. The screen of the display device includes horizontal rows of pixels. To display the pixels and, in turn, an image, an electron beam from the electron gun individually illuminates phosphors coating the inside of the screen by scanning the horizontal rows of pixels. There are two different types of well-known display devices, noninterlaced and interlaced.
In a noninterlaced display device, the electron beam scans each horizontal scan line of the screen once during each sweep of the screen. Each sweep of the screen is known as a display frame, a refresh cycle, a field, or generating a raster image. Noninterlaced display devices effectively operate on every pixel on each horizontal scan line of the screen as the electron beam sweeps across and down the inner surface of the screen. For example, for a 60 Hertz noninterlaced display device, every horizontal scan line of the screen is updated 60 times in a second.
In an interlaced raster display device, the electron beam updates, or refreshes, all odd-numbered scan lines in one sweep of the screen and all even-numbered scan lines in the next sweep of the screen, or vice versa. By refreshing alternate sets of lines on the display, interlacing halves the number of lines that must be updated in a single sweep of the screen and also halves the amount of information that must be carried by the display signal at any one time.
In the "DATALINK" system, the personal computer is programmed to display a sequence of display frames in which the horizontal scan lines represent individual bits of data to be transmitted. In this known system, an illuminated scan line represents a binary `0` and a non-illuminated scan line represents a binary `1`. To transmit data to the wristwatch personal information manager, the wristwatch is held near and facing the cathode ray tube. Each horizontal scan line appears as a pulse of a finite duration to an optical detector in the receiving wristwatch. Thus, data can be transmitted from the personal computer to the wristwatch personal information manager.
One drawback of the "DATALINK" system is that, when using a display device operating in interlaced mode, it is only possible to transmit on the even-numbered scan lines or odd-numbered scan lines, but not both. Thus, half of the scan lines of the display device operating in interlaced mode are not used to transmit data under the known methods. Therefore, there is a need in the art for a system that supports interlaced CRT data transmission in which both even-numbered and odd-numbered scan lines can be used to transmit data.